This invention relates to additives for hydraulic cement compositions. More particularly, this invention concerns additives for hydraulic cement which are particularly useful in Portland cement compositions such as masonry cements used to bond brick, block, etc.
Portland masonry cements are compositions produced particularly for use by masons in the bonding of bricks, blocks and the like. Such cements are typically mixed prior to use with a fine aggregate, usually sand, and water. It is desirable that the wet mortar have a high degree of plasticity for working (e.g. troweling) by the mason, as well as other desirable properties such as good "board life" (i.e. a long working time), water-repellancy, etc.
Masonry cements are produced by intergrinding Portland cement (containing gypsum for proper setting time regulation), with, generally, from about 35 to 65%, based on the total weight, of a solid material such as limestone, chalk, talc, pozzolans, clay, gypsum, or combinations of such. Limestone is most often the ingredient interground with the Portland cement because of its good plasticity enhancing properties. Such masonry cements are ground to a greater degree of fineness than most Portland cements intended for use in structural concretes. The finer grind of masonry cements improves the plasticity of the finished mortar products.
Additive products are sold for mixture with the masonry cement, such additive products being designed to impart certain desirable properties to the masonry cement composition. It is common practice to mix such additive products with the cement during the intergrinding of the cement with the gypsum, limestone, etc.
In U.S. Pat. Nos. 3,865,601 and 3,885,985 additive products of the above type are described. The additives described therein comprise an aqueous oil-in-water emulsion containing water, a water insoluble, water-repelling acid component (e.g. tall oil), an emulsifier (e.g. a salt of such acid), and a setting time-retarding agent (e.g. sucrose). This additive product is advantageously dispersible in water which reduces the risk of it being overdosed. The additive may also contain an air-entraining agent as an additional optional component.
An improved emulsion additive product is described in U.S. Pat. No. 4,375,987. In addition to the above-described constituents, this additive further comprises an emulsion stabilizer, (e.g. a glycol), which prevents the oil-in-water emulsion from destabilizing when exposed to freezing temperatures during shipping or storage prior to use.
The emulsion additive products described in the aforementioned patents have been successfully used to improve the water-repellancy and plasticity of Portland masonry cements. However, in order to obtain optimal plasticity and workability and extended board life it is often necessary to further add a water retention agent, such as a cellulose ether, during the grinding process. Conventional water retention agents cause the emulsion additives described above to destabilize and hence must be added as a separate feed stream, often as a dry powder. This method of addition is inconvenient, may increase manufacturing costs, and increases the risk of overdosing the batch with the water retention agent. These conventional water retention agents also may entrain large quantities of air, which may be undesirable where high strength is required.
Thus, it is desired to provide an emulsion additive which would, without the addition of a separate water retention agent, provide excellent water-repellancy, workability, plasticity, and other properties desired of masonry cements.